[AlotOfReading]

What the standard explicitly calls out as UB is only a small subset of actual UB.

While you can certainly classify all UB as "bugs", doing so misses the critical differences between UB and other categories of bugs. If you have a logic bug for example, your program will correctly and consistently do the wrong thing. It will continue doing that wrong thing with a different compiler, on a different platform today and 10 years from now. Implementation defined behavior is a bit looser, but will still be consistent with any particular implementation (which will document the behavior) and will only manifest in the code that depends on it. A PR inserting one of these "normal" bugs doesn't invalidate the entire rest of the program.

UB is different. You can't make assumptions about UB because from the point of view of the standard, UB is "not C". There are no assumptions to be made, it's just all the stuff that doesn't have assigned semantics. And since the input is meaningless, so is the entirety of whatever the compiler gives you back.

[coliveira]

> If you have a logic bug for example, your program will correctly and consistently do the wrong thing.

Not correct. Bugs can occur differently in different architectures, even in high level languages. UB is just a kind of bug whose effect depends on how the compiler behaves, so you have to be careful to test your code on different compiler settings. This is nothing new on programming languages, it is only made explicit in the C standard. Suddenly people started to believe that pointing out the obvious source of bugs (UB) in the standard is equivalent to let programs misbehave.

[AlotOfReading]

I'm not sure if you're making a point about "unspecified behavior" (where the compiler can choose between multiple valid behaviors), but no, a strictly conforming program will have the same semantics on different architectures. Strictly conforming programs can still have bugs, but their nature is completely different than UB because that's the point of the standard.

[adgjlsfhk1]

> you have to be careful to test your code on different compiler settings.

The problem is you have to test your code on compilers that don't exist yet with compiler settings that do different things from any compiler that ever might exist.

[coliveira]

This has always been the case. If you write code that has UB, new compilers can do something yet undefined, by definition.